The present invention is related to a method for the control of the blade pitch of a wind energy plant.
It is known to control the blade pitch in wind energy plants. In doing so, each rotor blade is shifted around its longitudinal axis in its blade pitch. At different blade pitches, the rotor blade takes out another moment from the wind at a time. The blade pitch control is particularly important in the full load operation, in which the control of the rotational number of the rotor takes place via the blade pitch.
Due to the continuously occurring variations of the velocity and of the direction of the wind, the blade pitch is continuously traced and adapted to a desired value preset by the operation management.
The blade adjustment of modern wind energy plants is driven via an ac motor, which is controlled by a converter. A proper drive can be assigned to each rotor blade. The motor acts on the rotor blade via a gearbox. Due to the frequent adjustment movements and the high mechanical stress of the blade bearings, the components of the blade adjustment experience a high wear.
From the European patent application EP 1 612 414 A2, the entire contents of which is incorporated herein by reference, a method has become known, in which a sudden downturn of the wind or a rapid shifting of the blade pitch is recognised by means of the trend of the blade pitch preceding a regulating intervention and the wind velocity. Because a sudden decrease of the wind velocity is often followed by an abrupt increase of the wind velocity, an excessive shifting of the blade pitch is avoided in these cases by limiting the shifting of the blade pitch with respect to its velocity or to a minimum blade pitch. By doing so, it is intended to reduce the stress of the rotor blades at a wind gust following a calm, for instance. However, this method does not exert any influence on the adjustment of the rotor blades in the normal operation, i.e, at relatively uniform conditions of operation, which do not require extraordinary large shifting movements.
On the basis of this, it is an objective of the present invention to provide a method for the adjustment of a blade pitch, which is material conserving and which reduces the stress of the components of the blade adjustment.